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Pilot Commands TOGA; A320 lands anyway

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Pilot Commands TOGA; A320 lands anyway

Old 31st May 2001, 08:39
  #21 (permalink)  
Tankengine
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Wink

Of course in a Boeing up elevator means up elevator and thrust lever forward means full thrust! [some things are meant to be simple!]
 
Old 31st May 2001, 08:52
  #22 (permalink)  
Icarus
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Updraft, downdraft, then tailwind.
Did anyone mention micro-burst?
I thought these things were easier for ATC/MET staff to spot (and hopefully report!)these days. Perhaps not in this case.
 
Old 31st May 2001, 15:40
  #23 (permalink)  
Flight Safety
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Heaven's Gate, the following quote is from the article:

<font face="Verdana, Arial, Helvetica" size="2">Wind conditions were significantly more severe than initially reported to the flight crew, with up and downdrafts and gusts that also involved an inversion of wind direction. The digital flight data recorder and additional inputs helped investigators determine that the A320 encountered strong tailwinds, a 1.25g updraft, then a downdraft followed at 50 ft. by a tailwind gust.

DURING THE UPDRAFT, the flight crew applied a forward side stick input, then aft input to reduce the aircraft's increasing sink rate. As the Ground Proximity Warning System (GPWS) sounded, they moved engine throttles to takeoff/go around power, but the aircraft nevertheless touched down, according to Capt. Michel Brandt. He is Airbus' deputy director of flight operations support. He added that the A320's estimated vertical speed, when it impacted the runway, was 1,200 ft./min.

The recently completed investigation has shown that the combination of up and down wind gusts and the flight crew's actions on flight controls led the aircraft to hit the automated systems' high angle of attack protection and prevented a normal flare.

The incident was reproduced here in a full-flight simulator and led Airbus to a decision to modify the AOA protection's control laws to increase the flight crew's authority.</font>
Your comments suggest that a windshear encounter of sufficient magnitude could not be overcome by the pilots. If the magitude of THIS windshear encounter exceeded the performance parameters of the aircraft thus making it impossible for the pilots to recover, then you're correct. No software mod of any kind can overcome the laws of aerodynamics.

But at least a couple of things can help the pilot as he nears the ground in a windshear encounter. The wind becomes more horizontal as the aircraft nears the ground, thus causing more of an airspeed/power problem than an AOA problem (assuming the aircraft has already flown past the center of the microburst). There's also the ground effect of the runway for extra lift if it's needed, while airspeed is being recovered for a go-around.

But if the windshear conditions are of insufficient force so as to allow the aircraft's attitude to be recovered, then the pilot MUST have precise control of the elevator (and throttles) to get out of the condition safely.

I'm convinced that this aircraft's attitude was recoverable and that the computer flew this aircraft into the ground, otherwise the software mod being proposed would be pointless.

------------------
Safe flying to you...
 
Old 31st May 2001, 16:01
  #24 (permalink)  
CaptSensible
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airforcenone, are you sure about what you wrote?

<font face="Verdana, Arial, Helvetica" size="2">this is done by the use of a 'soft' elevator which operates far more slowly than it should. (Notice next time you do your flight control checks how slowly the elevator moves relative to the stick movement).</font>
I understood that on the ground the a/c is in 'Ground Mode' and the stick to flight control relationship is a direct one (like in direct law in flight). Since the a/c normally operates in 'Normal Law' when airborne the 'G' demand is metered not by a 'slow elevator' but rather by the 1G computed by the ELAC?
 
Old 31st May 2001, 17:19
  #25 (permalink)  
gaunty
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Cool

Flight Safety
Wel put, in this case it sounds like the tail is wagging the dog.
 
Old 31st May 2001, 17:56
  #26 (permalink)  
Heavens Gate
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To Flight Saftey:

My initial reply was solely of technical nature. You wrote about the a/c being tricked into believing the AOA was too high, and about selecting TOGA and a suitable GoAround attitude below 200 ft will get you climbing in anything but an A320.
Remembering the doomed L1011 at Dallas (as well as many others) selecting TOGA and the proper attitude WILL NOT get you safely away from the ground if the energy and height required is less than the energy and height available. In case the a/c was rapidly approaching the stall AOA, adding further UP-elevator would only serve to increase the drag and trigger the stick-shaker in a non-Airbus fly-by-wire a/c (the pusher being disabled at such a low altitude). Therefore your choices would be limited to hitting the ground as controlled as possible on the shaker or stalling, going down uncontrolled, which the AOA-protection tries to avoid.
Please consider this reply again as technical, not as a pro-Airbus statement. But I have been part of some accident investigations in the past, and I can safely say that AOA-protection would have prevented some of those unfortunate accidents, as instant energy just isn,t available close to the stall - no matter how you got there.

Best regards ...
 
Old 31st May 2001, 19:15
  #27 (permalink)  
Heavens Gate
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Sorry I made a mistake. Of course it must read: ...if the energy and height required is more than the energy and height available.

Once again, sorry about that ... Best regards
 
Old 31st May 2001, 23:14
  #28 (permalink)  
airforcenone
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CaptSensible,

I must admit I may have got a little confused, however you have to admit that close to the ground, when you pull back fairly firmly, you want the bl**dy thing to go up! As you say, in flight the aeroplane is in Normal Law (ie. 1g trajectory). When it is on the ground, Direct Law applies (I think). During take-off, Direct Law 'blends' into Normal Law, however on landing it's one or the other. As far as I'm aware, this incident/accident occured before the aeroplane touched the ground. The other alternative is that it was in the flare, in which case, the aeroplane was trimming forwards to give the pilots something to pull against.

Someone feel free to put me right 'cos I do have a habit of digging big holes for myself!
 
Old 31st May 2001, 23:55
  #29 (permalink)  
Flight Safety
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Heavens Gate, I generally agree with you. If the energy and height required are greater than the energy and height available, then there's nothing you can do except to try and achieve a minimum rate of descent and a flat attitude on impact. Stalling the aircraft in an attempt to recover from windshear is also not helpful, and AOA protection would theoretically be useful in preventing this. But I emphasize the word theoretically.

I also agree that this really has nothing to do with Airbus or any other manufacturer. This is really about an aircraft designed with a particularly unique feature called "Alpha Protection" that has "Alpha Floor" and "Alpha Max" modes.

Apparently during the simulator portion of this accident investigation, it must have been determined that the AOA was not calculated properly due to the sequence of updrafts, downdrafts, and changing airspeeds from gusts and "wind direction inversions" just prior to the flare. If the AOA was not calculated properly, then the "Alpha Protection" is of no help to the pilot, and in fact may hinder his ablility to recover the aircraft if sufficient height and energy ARE available for recovery. I think that's precisely what occurred here, and that's why the investigation has recommended modifying the software to give the pilots more direct control in the flare.

But this software mod poses some interesting questions. On the one hand I see this mod as perhaps partially negating the benefits of AOA protection. On the other hand, if the rapidly changing wind conditions that existed in this accident prevent the possibility of accurately and reliably calculating the AOA, then a switch to Direct Law would be the preferred solution. What I'm not clear on is whether this software mod will cause a reversion to Direct Law in all cases just prior to the flare, or only in cases where rapid changes in wind direction cross a threshold of AOA calculation "unpredictability", thus forcing a reversion to Direct Law in only those instances.

------------------
Safe flying to you...

[This message has been edited by Flight Safety (edited 01 June 2001).]
 
Old 1st Jun 2001, 01:32
  #30 (permalink)  
Heavens Gate
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To Flight Safety:

It is good to see that at least some professionals are left on pprune who are able to discuss a topic in a respectful and openminded way - my respect to you.

Best regards ...
 
Old 1st Jun 2001, 06:40
  #31 (permalink)  
411A
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AirBus seem to make changes to the software every time there is an incident/accident. Surely the question must be.....WHY was it not designed properly in the first place? Altho the A320 was the first FBW airliner and a certain amount of "adjustment" was needed from time to time, surely now that it has been around for a long time and is a mature design, was it perhaps designed initially around a flawed principle? The B777 does not seem to have these same type of "problems".
 
Old 1st Jun 2001, 06:59
  #32 (permalink)  
Flight Safety
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411A, the Boeing FBW system of "envelope protection" uses pitch control to maintain airspeed, rather than using pitch control to maintain an AOA value. It's a fundamentally different approach, although I must admit I understand the Airbus system better than I understand the Boeing system.

Because the basic approach to "envelope protection" is fundamentally different between the designs, the possibilities and permutations MUST be different when flight occurres near the "edge" of the envelope. These are the areas of flight where the weaknesses of either design will be exposed.

Now I want to go learn more about the Boeing system...
 
Old 1st Jun 2001, 08:13
  #33 (permalink)  
Diesel8
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FS,

Perhaps the fix will be similar to the one used in abnormal attitude law (?).
 
Old 1st Jun 2001, 08:55
  #34 (permalink)  
Ignition Override
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Arrow

411A raised a very good question, and I know nothing about fly-by-wire. AS for angle-of-attack info, aren't there conflicts between any system which tries to protect us from terrain (GPWS-old, or new EGPWS) and at the same time protect us from windshear, since there must be a priority?

It seems a little strange to me that the US FAA (CAA etc?) never required a true angle of attack indicator system (with precise limits) for US transport aircraft, however the FBW Airbus or Boeing flight control computers appear to know the desired AOAs at all times. AOA would be much better than using airspeed and pitch, but I doubt that the optimum or max lift AOA is displayed on any modern ADI or PFD, knowing that the FAA has no desire to develop a program for this (too much $?). The US AIR DC-9 windshear recovery procedures at Charlotte (CLT) were seriously hindered by input during changing flap positions, and by weather/wind info not being quickly shared between controllers on different frequencies at the same airport facilities.

Is it likely that several crashes might have been avoided if a user-friendly AOA system (with training on it) had been in use for decades on civil and military transports, as on military tactical and trainer jets?
 
Old 1st Jun 2001, 09:01
  #35 (permalink)  
screwjack
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Thumbs up

Ignition Override:

An AoA indication is available at AI as an extra option, for an extra price. Some former Air Inter A 320 have this feature installed. I beleive the a/c are now with AF.
Rgs

screwjack
 
Old 1st Jun 2001, 13:06
  #36 (permalink)  
Burger Thing
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Hi 411A, you wrote:
<font face="Verdana, Arial, Helvetica" size="2">AirBus seem to make changes to the software every time there is an incident/accident. Surely the question must be.....WHY was it not designed properly in the first place? </font>
The Airbus is an highly computerized airplane. Airbus made this approach in the believe and goodwill to increase saftey: reducing pilots workloads, providing crew, passengers and aircraft with all kind of safety systems, some of them even overrides wrong pilots inputs.

But this philosophy is not free of risks. Like any other computer system, Soft- and Hardware designers are given in the beginning of their work a specification envelope. Based on this specifications, they create, design, build Hardware and write Software. The varification process comes afterwards, to see and check, if all the systems work properly under all circumstances WITHIN the given speficication envelope. The flight test is also part of this varification process.

The ideal case is, that on every given input (within the specifications) the computer produces a correct output. In an aircraft computer system this means, that the Hard- Software senses for example dangerous situations (input) and takes corrective action (output). Ideally these systems works great and increase saftey dramatically. But only within the given specification envelope!

And here lies the danger of Airbus philosphy and in fact of every automated system: Something occurs outside the specification envelope which has not been foreseen by the engineers, computer designers, etc. This can be in case of an aircraft weather phenomena, technical defects, runway conditions, or a combination of everything, etc.

The worst case scenario is, that the pilot can't react to this situation, because the computer doesn't allow him/her to do so, because the computer does not see this specific input, thread, or situation.

Because of this reason, we see after almost every Airbus incident/accident a change in Soft- and Hardware. Guys, don't get me wrong. I don't want to contribute in an emotional Airbus vs. Boeing clash. But I just hope, the engineers have prepared and designed the systems on an Airbus in a way, that in a couple of years, when the A320 is flown somewhere as a cheap old model (maybe to replace an old 737-200 ) in a third world operator (maybe in poor technical conditions), it brings the people on board safely from A to B.
 
Old 1st Jun 2001, 13:14
  #37 (permalink)  
Heavens Gate
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One of those a/c is on short term lease to us from Air France. However, as this AOA indicator does not have any limit markings on it, it is of limited use only.

To 411A: the fly-by-wire system in the 777 is of a much simpler design, so may be that is the reason it doesn,t have as many teething problems. As I have stated before, on a day to day basis I prefer to fly the 777, but when reaching any limit I still prefer the Airbus way of keeping me out of trouble.
 
Old 1st Jun 2001, 15:44
  #38 (permalink)  
ex-expat
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Guys,
Seems to me the Airbus FBW system is that the pilots make an imput on the controller and that is their vote. Then the three computers vote. Then the airplane does something...maybe.

The B-777, the pilots have veto power and the control surfaces will move if you insist. A very different design philosophy if you will.

At Airbus, pilots are a necessary political problem to overcome as they are always out their crashing their perfectly designed and thoughtout airplanes. See the movie German TV documentry "Fatal Logic" and you'll understand what the powerful EU engineers at Airbus think of your skills and judgment as a pilot.
 
Old 1st Jun 2001, 18:24
  #39 (permalink)  
electricjetjock
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Red face

We are all speculating here ( and I am about to add my twopenny worth) but yet again it has developed into A Vs B.


1. Why was GA action not taken immediately!

2. If idle had been commanded as part of the flight path correcting actions, then you can select TOGA but you are not going to get it in 1 to 2 seconds! The time available before ground impact is not there.

3. If the aircraft did not have AOA / Stall protection. Then all you guys saying that you want the controls to do what you ask, would have had the nose come up (making you feel good), stalled the aircraft, increased the ROD and impacted the runway tail first and we can all guess the outcome of that!

What a lot of you seem to forget is that the americans did it first with the F16. Also there was a lot of design input to the 777 by a few dino's in the US majors. Otherwise why would you have that great control wheel to turn a few electrical transducers!! not forgetting the other control wheel.

------------------
Keep smiling!!!!
 
Old 1st Jun 2001, 21:52
  #40 (permalink)  
Tarmach
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I have zero hours on any Airbus, i'll be the first to admit it! But what are thay trying to pull over pilots. For instance I can't believe anyone really likes that sidestick, it seems more of a gimmick to enable airbus to sell more aeroplanes than a real aid to the pilot- so what the pilot has more leg room- whoophy!! Further, with any normal yoke when the A/P is connected the pilot can tell exactly what the aeroplane is doing just by placing their hands on the control column, however, with that stupid sidestick you can't tell jack s*** whats happening. In addition to this the throttles don't move either, when the A/T is engaged. Give me a Boeing any day, airbus has LOST THE PLOT!! Apologies for going slightly off-topic!
 

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